r. a. de hon 2011 gsa annual meeting crater morphologies in monogenetic volcanic fields of western...

R. A. De Hon

2011 GSA Annual Meeting

CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN

NEW MEXICO

THE SIGNIFICANCE OF MAARS ON EARTH AND MARS

R. A. De Hon2011 GSA ANNUAL MEETING

Rebranded

THIS PRESENTATION

• As original title states… Morphology of landforms in three monogenic volcanic fields in western New Mexico

• Specifically, the morphology of… Maar craters Tuff cones Cinder cones

• Located in …New Mexico:Red Hill-Quemado Volcanic Field

Bandera Volcanic Field Mt. Taylor-Mesa Chivato Volcanic Field

WITH SPECIAL ATTENTION TO MAAR CRATERS

• Maar craters are formed when magma encounters groundwater. The resultant steam explosion excavates a bowl-shaped pit surrounded by a tuff ring that resembles a meteorite crater.

• The term maar comes from a Franconian dialect for lake derived from the Latin “mare” (sea).

• In the type locality—the Efiel Region of Germany— the craters extend below the water table and are occupied by lakes.

• Maar craters range in size from a few hundred meters to several kilometers in diameter.

• Their eruptive history consists of repeated venting over a period of weeks or months.

CREDITS – PREVIOUS WORKERS

• Jayne C. Aubele

• Larry S. Crumpler

• A. W. Laughlin

• P. W. Lipman

• C. Maxwell

• And many others

WHY DO WE CARE?

• Early ejecta in maar craters contain accidentals from underlying strata.

• Occasionally the ejecta incudes mantle xenoliths.

• Maare on Mars may be unique sites to obtain deep crustal samples.

Mantle xenolithKilbourne Hole, NM

ULTIMATE OBJECTIVES

• Volcanic morphometry with attention to explosive craters and transitional forms

• Early ejecta as sampling of subjacent rock materials

• Magma, vapor, country rock interactions and final crater morphology

• Application to Mars volcanic craters and possibility of maar craters as crustal sampling sites

This talk

Mesa Chivato

Bandera (Malpias)

Red Hill MAAR CRATERSin Northeast New Mexico

N

100 km

CHAIN OF CRATERSBANDERA FIELD

Maar

ZUNI SALT LAKE

1 km

CERRO AMERICO

1 km

EXAMPLE: CINDER CONE—CERRO AMERICO

Basal Diameter 1 237 metersCrater Diameter 269 Cone Height 118 Crater Depth 41

BANDERA CRATER

1 km

EXAMPLE: TUFF RING—BANDERA CRATER

Basal Diameter 1156Crater Diameter 556Rim Height 128Crater Depth 156

HEUCO CRATER

1km

EXAMPLE: MAAR—HUECO

Basal Diameter 1150 metersCrater Diameter 718Rim Height 75Crater Depth 98

Scoria mound

CD

Cd

Curve is best fit to Red Hill and Mesa Chivato data

Tuff Rings

Depth vs. Height

Base surgeand Air Fall—Reworked shallow sublacent material

Vent Opening Breccia—Most of the subcrater xenoliths are found here.

PRISTINE

Tuff Ring

Maar

Cinder cone

VOLCANIC CENTRAL VENT VARIATIONS

1 km

All profiles to same scale.

Variation in size is chiefly due to the duration of eruptions and volume of material ejected.

Constituents of the eruption changes as eruption progresses…

Lava

Scoraceous cinders

Epiclastic tuff

Early xenolith-rich breccia

VENT MORPHOLOGYA FUNCTION OF

• Composition of magma and volatile content of magma• Depth of magma and groundwater interaction• Volatiles in country rock

• Connate water• Groundwater• Ground ice

• Continuing activity• Pyroclastic• Lava

• Resistance of country rock• Slumping during eruptive phase• Degradation following eruption

Highly eroded -or-Blew its top?

Crater-in-crater

Rimless depression

RED HILL MAARwith internal cinder cones

Cone filling maar

Renewed activity Pristine Degraded

Cone filling maar Tuff Ring Breached crater

Cone-in-maar Maar Rimless depression

Explosion crater? Cinder cone Scoria Mound

VOLCANIC CENTRAL VENT VARIATIONS

1 km

All profiles to same scale.

SO, THE POINT IS…

• Earliest maar ejecta provide a sampling of substrate materials.

• Those materials may be preserved in a variety for subsequent structures.

• Some day, in future exploration of Mars, maare will be important sites to visit and sample.

Mars Volcanic field

THANK YOU